Topex Altimetric Mean Sea Level and Gravimetric Geoid in the North of Algeria

Abstract

The mean sea level is processed from Topex altimetric measurements collected on the Algerian coasts (on the South West of the Mediterranean Sea) over a three months period (April 20 to July 28, 2000). The model used, based on the Barrick-85 model, determine the instantaneous sea surface heights for 80 cycles distributed on 8 orbital arcs. The pre-processing of the raw data permit the selection about 75 % of the measurements. The processing of the fitted data, by polynomial adjustment, is done after the correction of the main disturbed effects (instrumental, atmospheric,...) and the reduction of the radial component of the orbital error. The analysis of the mean arcs in the crossing points by the least squares adjustment allows a centimetric accuracy of the mean sea level. The surface obtained was extrapolated to the North of Algeria (surrounding the coasts) and compared to a gravimetric geoid calculated with a set of BGI free air gravity anomalies and GETECH data using the FFT techniques implemented in the Geofour program (Tscherning, 1994). The metric difference obtained is due to the insufficient altimetric and gravimetric data distributions, and to the extrapolation method used. The availability of an exhaustive gravity measurement, particularly the gravity cruise data (sea data), and a long period altimetric measurement, will allow a strong comparison between the surfaces.